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Question on WC Gen2 vs Gen3 w/Solar+PW

dsss

Member
Jan 29, 2018
40
24
Bay Area
Hi,

My apologies as I may not have all the technical details correct but I just completed a Solar Roof (8kw) +2 PW install here in the Bay Area.

We have a M3 and a Gen2 Wall Charger. When we plug the charger into our M3, the load pulling from the grid is about 10-11kw and is causing our main breaker to trip (we are being taken off the grid). Tesla is still troubleshooting this but their current working theory is that the load balancing in the Gen2 charger is insufficient and I need to upgrade to a Gen3 charger which according to them offers more sophisticated load balancing to support our system. Alternatively, I could shift the charger off the solar/backup setup but that would seem to limit our options in case of emergency needs.

Beyond the cost, moving to the Gen 3 is problematic as we use the full length of the Gen 2 charger (Gen 3 is six feet shorter), I'm just confused why we're having such an issue with the Gen2 charger in our setup?

I'm confused and would greatly appreciate any guidance or insight this community could offer.
Thanks!
 

miimura

Well-Known Member
Aug 21, 2013
6,353
6,052
Los Altos, CA
Makes no sense to me. What is the aggregate load on the main breaker when it trips? You can probably get the value from the meter just before it trips. If not, a peak hold clamp ammeter would be valuable to check whether the breaker is tripping appropriately or not. Most likely, the problem will go away if you replace the main breaker.

Load balancing in the wall connector only comes into the picture if you had more than one wall connector. You didn't mention that was the case. Therefore Gen2 vs. Gen3 is a red herring.
 
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dsss

Member
Jan 29, 2018
40
24
Bay Area
Thanks, the Tesla app was showing roughly 11kw of load. Tesla did actually replace one of the main breakers (125a) and the one that was tripping but within 30 minutes of plugging the car back in, it tripped again.
 

Vines

Active Member
Jul 20, 2018
1,902
2,242
Silicon Valley, CA
Load balancing is making sure your L1 and L2 are drawing a similar amount. If either leg pulls more amps than the breaker rating, it will trip.

I do not know why the Gen 3 Wall charger will help. I suspect it wont do much, unless they reduce the charge rate, but they could do that with the Gen2 no problem so I don't really understand. Its good to have replaced the main CB just in case it was bad. If you are generating enough heat to pop the main you might melt your service conductors...you really don't want to do that so you should fix this asap. In the meantime, drop your charge rate to 24A or so is my recommendation.

It sounds like your house +charger is pulling too many amps. You need to reduce the draw on either one. Popping the main breaker is no joke and you need to be careful. The first thing I would do is look for hot spots in the service panel, and look at my smart meter to see if I was truly pulling enough to pop the main.

Then I'd measure draw on both legs and see if they are unbalanced. Its possible that you could shift some breakers around so heavily used circuits were relocated to the lightly used service leg.
 

dsss

Member
Jan 29, 2018
40
24
Bay Area
Thanks, I'm a total electrical novice so all of that sounds beyond my skill/knowledge set but I get the general idea that i'm putting too much strain on my panel. If that was the case, why has it worked fine for years with my car charger and the same house demand, the only difference now is the addition of my Tesla panel supporting the solar roof and PWs. From a demand standpoint, nothing has elevated?

For now, they pulled the car off the solar/backup circuit (so I no longer even seen the draw in the tesla app) and everything seems stable, which is good, but I can't charge the car from the solar/PW if needed.

Also, I super appreciate all the help. Thank You!
 

Electrph

Member
Aug 29, 2019
426
280
Central California
have to agree with @Vines his electrical knowledge esp in area of solar / home battery backup I'm sure is greater than mine but based on what I know of gen 2 vs gen 3 connector I see no way this upgrade would solve this problem. In fact at this time I know of no advantage of gen 3 over gen 2 and gen 3 has seen many early and continuing issues. Gen 3 has potential in future via updates pushed to it.
 

CrazyRabbit

Member
Apr 21, 2020
414
126
Fort Worth TX
Need a wiring diagram with the loads on panel to diagnose.
But if I read correctly a 125 amp sub panel breaker is tripping. And breaker was replaced so I have to think it is overloaded.
WC is only a fancy plug and charger is in car, to that end only reducing the charge current will help
11Kw is 45 amps! So if you have a high electric heat load and electric water heater running at the same time, it my trip.
i'm guessing your installer de-rated your main breaker for backfeed and did NOT install a generation panel.
 
Last edited:

BGbreeder

Member
Jun 19, 2020
292
178
Bay Area
I'm with @Vines. Popping a 125Amp breaker is serious.

If you are an electrical novice, I would get a professional out sooner rather than later.

And no, I really don't think that getting a Gen 3 charger is the right way to go, even if it were to solve your problem. Your gen 2 charger is pulling a fraction of your 125Amp breaker.

All the best,

BG
 

dsss

Member
Jan 29, 2018
40
24
Bay Area
Thanks everyone for the helpful suggestions here. To close this out (I hope!), it took a couple of additional onsite visits from the Tesla electrical team but they believe it was the specific brand of breaker they installed that was the culprit. The first breaker they installed didn't work well with the existing panel and flipped whenever a particularly heavy load came in (i.e. the car charging and/or the hot tub motor kicking in). We swapped it with another breaker brand and for the past 2-3 days, have been running soundly without issue, including car charging and running the tub at the same time as a stress test.

They also had the engineering staff re-run our load balance to make sure all their calculations were accurate and safe and they confirmed the math was right. So if this occurs again, I think then we take a hard look at the panel itself. I'm optimistic however that this has resolved the issue. Thanks again for the insights and support!
 

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